Modified k-ω model using kinematic vorticity for corner separation in compressor cascades

Recently bimodal phenomenon in corner separation has been found by Ma et al. (Experiments in Fluids, 2013, doi:10.1007/s00348-013-1546-y). Through detailed and accurate experimental results of the velocity flow field in a linear compressor cascade, they discovered two aperiodic modes exist in the corner separation of the compressor cascade. This phenomenon reflects the flow in corner separation is high intermittent, and large-scale coherent structures corresponding to two modes exist in the flow field of corner separation. However the generation mechanism of the bimodal phenomenon in corner separation is still unclear and thus needs to be studied further. In order to obtain instantaneous flow field with different unsteadiness and thus to analyse the mechanisms of bimodal phenomenon in corner separation, in this paper detached-eddy simulation (DES) is used to simulate the flow field in the linear compressor cascade where bimodal phenomenon has been found in previous experiment. DES in this paper successfully captures the bimodal phenomenon in the linear compressor cascade found in experiment, including the locations of bimodal points and the development of bimodal points along a line that normal to the blade suction side. We infer that the bimodal phenomenon in the corner separation is induced by the strong interaction between the following two facts. The first is the unsteady upstream flow nearby the leading edge whose angle and magnitude fluctuate simultaneously and significantly. The second is the high unsteady separation in the corner region.

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LES Investigation of Boussinesq Constitutive Relation Validity in a Corner Separation Flow

Volume 2C: Turbomachinery ◽

10.1115/gt2018-75792 ◽

2018 ◽

Author(s):

Jean-François Monier ◽

Nicolas Poujol ◽

Mathieu Laurent ◽

Feng Gao ◽

Jérôme Boudet ◽

...

Keyword(s):

Strain Rate ◽

Stress Tensor ◽

Reynolds Stress ◽

Constitutive Relation ◽

Strain Rate Tensor ◽

Separation Flow ◽

Compressor Cascade ◽

Corner Separation ◽

Reynolds Stress Tensor ◽

Mean Strain

The present study aims at analysing the Boussinesq constitutive relation validity in a corner separation flow of a compressor cascade. The Boussinesq constitutive relation is commonly used in Reynolds-averaged Navier-Stokes (RANS) simulations for turbomachinery design. It assumes an alignment between the Reynolds stress tensor and the zero-trace mean strain-rate tensor. An indicator that measures the alignment between these tensors is used to test the validity of this assumption in a high fidelity large-eddy simulation. Eddy-viscosities are also computed using the LES database and compared. A large-eddy simulation (LES) of a LMFA-NACA65 compressor cascade, in which a corner separation is present, is considered as reference. With LES, both the Reynolds stress tensor and the mean strain-rate tensor are known, which allows the construction of the indicator and the eddy-viscosities. Two constitutive relations are evaluated. The first one is the Boussinesq constitutive relation, while the second one is the quadratic constitutive relation (QCR), expected to render more anisotropy, thus to present a better alignment between the tensors. The Boussinesq constitutive relation is rarely valid, but the QCR tends to improve the alignment. The improvement is mainly present at the inlet, upstream of the corner separation. At the outlet, the correction is milder. The eddy-viscosity built with the LES results are of the same order of magnitude as those built as the ratio of the turbulent kinetic energy k and the turbulence specific dissipation rate ω. They also show that the main impact of the QCR is to rotate the mean strain-rate tensor in order to realign it with the Reynolds stress tensor, without dilating it.

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Clast-based kinematic vorticity gauges: The effects of slip at matrix/clast interfaces

Journal of Structural Geology ◽

10.1016/j.jsg.2009.07.008 ◽

2009 ◽

Vol 31 (11) ◽

pp. 1322-1339 ◽

Cited By ~ 55

Author(s):

Scott E. Johnson ◽

Hendrik J. Lenferink ◽

Nancy A. Price ◽

Jeffrey H. Marsh ◽

Peter O. Koons ◽

...

Keyword(s):

Kinematic Vorticity

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Control of the Corner Separation in a Linear Cascade by Trailing Gaps

Volume 2A: Turbomachinery ◽

10.1115/gt2017-65158 ◽

2017 ◽

Author(s):

Wenfeng Zhao ◽

Bin Jiang ◽

Qun Zheng

Keyword(s):

Flow Field ◽

Suction Surface ◽

Optimal Length ◽

Corner Separation ◽

Linear Cascade ◽

High Loss ◽

Axial Compressors ◽

Pressure Surface ◽

Sst Turbulence Model ◽

The Stability

Hub corner is the high-loss area in the blade passages of turbo machinery. It is well known that the flow separation and vortex development in this area affects directly not only the energy losses and efficiency, but also the stability of axial compressors. Linear compressor cascades with partial gaps and trailing gaps which can blow away the corner separation by the pressure difference between the suction surface and pressure surface are numerically simulated in this paper. A proposed linear cascade model with gaps has been built. The steady flow field in a linear cascade with different length gaps is studied by numerical simulation of RANS with SST turbulence model and γ-Reθ transition model focusing on the streamline structure between the corner separation vortex and the gap leakage vortex, especially the interaction of the two vertical vortex. When the length of trailing edge gaps is enough (in this paper, the optimal length of the gap is 30% chord), the corner vortex basically disappears completely. At the same time, the mode of flow field changes from the closed separation to the open separation.

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Improved compressor corner separation prediction using the quadratic constitutive relation

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1177/0957650917709367 ◽

2017 ◽

Vol 231 (7) ◽

pp. 618-630 ◽

Cited By ~ 3

Author(s):

Xinrong Su ◽

Xin Yuan

Keyword(s):

Constitutive Relation ◽

Eddy Viscosity ◽

Pressure Coefficient ◽

Momentum Equation ◽

Viscosity Model ◽

Corner Separation ◽

Pressure Loss Coefficient ◽

Eddy Viscosity Model ◽

Relation Model ◽

Separation Size

This work presents the implementation and study of the quadratic constitutive relation nonlinear eddy-viscosity model with representative compressor application, for which the corner separation has been poorly predicted with the widely used linear Boussinesq eddy-viscosity model. With the introduction of the Reynolds stress anisotropy, the secondary flow of the second kind and its effect on the corner flow can be well captured and this results in greatly improved prediction of pressure coefficient, total pressure loss coefficient and the corner separation size. Without the quadratic constitutive relation model, the separation size and loss are generally over-estimated. The mechanism of the improvement is studied using both the vortex dynamics and the momentum equation. It is proved that quadratic constitutive relation model consumes low CPU time and provides much improved compressor corner separation prediction without worsening the convergence property.

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Identification of corner separation modelling in axial compressor stage

E3S Web of Conferences ◽

10.1051/e3sconf/202017801035 ◽

2020 ◽

Vol 178 ◽

pp. 01035

Author(s):

Sergey A. Serkov ◽

Viacheslav A. Sedunin ◽

Vitalii L. Blinov ◽

Oleg V. Komarov ◽

Yurii M. Brodov

Keyword(s):

Fluid Dynamics ◽

Axial Compressor ◽

Separated Flows ◽

Operating Point ◽

Compressor Stage ◽

Main Interest ◽

Corner Separation ◽

Computation Fluid Dynamics ◽

Operation Conditions

The paper presents a study of corner separations in hub to blade region at various operation conditions towards compressor stall. It is known that for compressor flows with low or none separations computation fluid dynamics with RANS methods work quite well, however, for highly separated flows they are no longer entirely valid. Therefore, several criteria were applied for prediction and quantification of possible corner separation, and the main interest of this work is in predicting the separation just before it will actually happen by certain flow metrics, so these metrics can be further used as a ‘pre-stall’ criteria whilst the RANS CFD operating point still behave within its appropriate limits. Also the effect of shear lean is discussed in the presented context.

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Investigation of Vortical Structures and Turbulence Characteristics in Corner Separation in an Axial Compressor Stator Using DDES

Energies ◽

10.3390/en13092123 ◽

2020 ◽

Vol 13 (9) ◽

pp. 2123

Author(s):

Jun Li ◽

Jun Hu ◽

Chenkai Zhang

Keyword(s):

Three Dimensional ◽

Axial Compressor ◽

Suction Side ◽

Turbulence Energy ◽

Separation Flow ◽

Mechanism Analysis ◽

Separation Region ◽

Detached Eddy Simulation ◽

Vortical Structures ◽

Corner Separation

In order to investigate the flow structure and unsteady behavior of three-dimensional corner separation, a delayed detached-eddy simulation (DDES) method based on the Spalart–Allmaras (SA) model is performed on the third-stage stator of a multistage low-speed axial compressor. The stator simulation is validated by experiments before flow mechanism analysis. The complicated flow fields in the stator are then described step by step. Firstly, the structure and development process of vortices in corner separation flow are analyzed. Secondly, the velocity histogram of the monitor points in the mainstream and corner separation regions is obtained, and the velocity distribution of the corner separation region is discussed. Finally, Reynolds stress, Lumley anisotropy, turbulence energy spectra, and helicity density are discussed to understand the turbulence behavior of the corner separation flow in the stator. The results show that the corner separation appears at even the design condition and different kinds of vortical structures appear in the stator hub corner. The unsteadiness of corner separation flow is mainly reflected in the separation on the suction side of the blade and the wake shedding. Turbulence anisotropy and energy backscatter are found to be dominant in the separation region, which is correlated to the high shear stress.

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Effects of Endwall Profiling on Axial Flow Compressor Stage

Volume 7: Turbomachinery, Parts A and B ◽

10.1115/gt2009-59418 ◽

2009 ◽

Cited By ~ 4

Author(s):

Jialing Lu ◽

Wuli Chu ◽

Yanhui Wu

Keyword(s):

Flow Field ◽

Engineering Design ◽

Axial Flow ◽

Design Tool ◽

Operating Conditions ◽

Compressor Stage ◽

Corner Separation ◽

Axial Flow Compressor ◽

Flow Compressor ◽

Stage Efficiency

In recent years endwall profiling has been well validated as a major new engineering design tool for the reduction of secondary loss in turbines. However, its application on compressors have been rarely performed and reported. This paper documents the findings of the analysis for diminishing compressor stator corner separation using endwall profiling; In the study, novel profiled endwalls were designed and numerically studied on a subsonic axial-flow compressor stage. The compressor stator endwalls were profiled on both axial and azimuthal directions. The results showed, the stator corner separation was significantly suppressed under all the operating conditions by implementing this profiled endwall. Significant improvements on stage pressure ratios and stage efficiency were observed. Detailed flow field changes, as well as endwall profiling methods are provided in the paper, so that the results of this research can be referenced to other compressor designs.

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